Alcohol hand sanitizers, the mainstay of hand hygiene in healthcare settings, do not have activity against bacterial spores. This gap in the spectrum of activity of alcohol is of critical importance because the spore-forming anaerobe Clostridium difficile is a major pathogen in healthcare facilities and in the community. Because currently available sporicidal disinfectants are too harsh for routine use on skin, we have investigated the novel approach of inducing sporicidal activity in alcohol and other skin disinfectants by combining them with agents that alter the spore to allow them to reach their target. We have demonstrated that acidification of alcohols (pH 1.5 to 2) results in rapid sporicidal activity against C. difficile in vitro and on skn. The goal of this proposal is to develop formulations of acidified ethanol with optimal safety and tolerability and to determine the degree of reduction in spore viability that is necessary to prevent transmission. Our central hypothesis is that modified acidified ethanol solutions that reduce C. difficile spore recovery by 97% or more on hands of volunteers will be effective in preventing transfer of spores from the hands of healthcare personnel. Our first specific aim is to identify modifications of acidified ethanol that optimize safety and tolerability on skin while maintaining efficacy against C. difficile spores. To accomplish this aim, we will examine strategies to enhance the sporicidal activity of acidified ethanol, including increased ionic strength, addition of diluteperacetic acid, and mild temperature elevation, and test the effectiveness of optimized solutions in an ex vivo porcine skin model and on hands of human volunteers. Our second specific aim is to determine the effectiveness of acidified ethanol solutions for prevention of transfer of C. difficile spores from the hands of healthcare personnel. To accomplish this aim, we will determine the effectiveness of acidified ethanol solutions in reducing transfer of spores from hands of volunteers in lab simulations and from hands of healthcare personnel. The results will be significant because C. difficile is a major cause of morbidity and mortality and there is an important unmet need for development of sporicidal hand hygiene products.